10 binders cost $10.10. Which equation would help determine the cost of 2 binders?
Solution: There are several equations that could help determine the cost, each with a slightly different approach. Let $x$ represent the unknown cost of 2 binders. Since 2 binders cost $x$ , we have the following proportion: $\dfrac{2}{x}$ We can write the fact that 10 binders cost $10.10 as a proportion: $\dfrac{10}{\$10.10}$ The cost changes along with the number of binders purchased, and so the two proportions are equivalent. $\dfrac{2}{x} = \dfrac{10}{\$10.10}$